Technology utilized for providing heating surfaces has changed dramatically over time. One example of a material utilized for fabrication of heating surfaces is glass ceramics. Glass ceramics are useful for use as heating surfaces since glass ceramics provide a smooth and hard surface that may easily be cleaned, they are chemically stable at cooking and boiling temperatures, and due to glass ceramics typically having a low coefficient of thermal expansion, they are resistant to thermal shock.
Examples of heating systems that utilize glass ceramics include, but are not limited to, cook tops and laboratory hot plates. Typically, these heating systems utilize a large radiant heater as a heat source that is positioned below a surface of a material, such as a nickel chrome resistive element, used as a heating platform.
Unfortunately, use of present glass ceramic heating systems having a heating source positioned there below, is thermally inefficient. Specifically, the nickel-chrome resistive element has a thermal emissivity of approximately sixty percent (60%) or less, while the glass ceramic has a thermal transmittance of approximately eighty percent (80%) or less. In addition, a pot, or other device utilized for heating a substance therein, is required to be engineered in a shape and have surface properties that allow for high thermal absorption.
Attempts have been made to make heat transfer associated with the abovementioned glass ceramic heating system predominantly conductive. As an example, U.S. (U.S.) Pat. No. 4,039,777 (hereafter, “the '777 patent”), issued Aug. 2, 1977, to Fred E. Baker, discloses a heating system fabricated by cementing resistive heating wires to the glass ceramic, positioning wire elements contained within an insulating structure next to the glass ceramic, and configuring sheath type elements so that heat is conducted to the glass ceramic. Unfortunately, the heating system of the '777 patent is not thermally efficient. Specifically, the '777 system utilizes resistive heating wires located within a cement layer. The heating wires are intended to heat the entire cement layer. When the cement layer is heated, the heat is conducted to the glass ceramic. Unfortunately, heat is lost throughout the cement layer, thereby resulting in poor thermal efficiency. In addition, heat is poorly, and unevenly, displaced in the '777 patent system since the portions providing heat are limited to the heating wires, which are spaced apart a predetermined distance.
One example of a heating system is categorized as a thick film heater. U.S. Pat. No. 6,037,574, issued Mar. 14, 2000, to Lanham, et al., discloses an example of a thick film heater, which contains noble metals in a glass paste deposited on quartz, wherein, as is known by those having ordinary skill in the art, quartz is a low thermal expansion glass, or glass ceramic. In addition, Watlow Electric Manufacturing Company of St. Louis, Mo. manufactures thick film heaters. Unfortunately, thick film heaters suffer from performance problems due to a lack of molecular bonding of the paste to the glass ceramic. The lack of molecular bonding may result in poor thermal conductivity. Specifically, the coefficient of thermal expansion of the noble metal paste does not match the coefficient of thermal expansion of the glass ceramic, thereby resulting in cracking between the paste and the glass ceramic after repetitive heating and cooling of the thick film heater.
Another example of a heating system is categorized as a thin film heater. U.S. Pat. Nos. 5,616,266, issued Apr. 1, 1997, to Richard Cooper, and 6,376,816, issued Apr. 23, 2002, to Cooper, et al., disclose examples of thin film heaters. In addition, Thermo-Stone USA, LLC, of Marina, Calif. manufactures radiant thin film heaters. Unfortunately, thin film heaters do not deliver adequate power to provide for efficient use in cook top applications. Specifically, sputtering, evaporating, chemical vapor deposition (CVD), or other techniques of providing a thin film heater are inadequate because the resulting thin film heater does not provide adequate conductance properties to allow normal and high voltages, and associated currents, to be accommodated for by the resulting thin film heater.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies.